Meeko the calf stood nuzzling a pile of hay. He didn't seem to have much appetite, and he looked a little bored. Every now and then, he glanced up, as though wondering why so many people with clipboards were standing around watching him.Fourteen hours earlier, I'd watched doctors lift Meeko's heart from his body and place it, still beating, in a plastic dish.

He looked no worse for the experience, whisking away a fly with his tail as he nibbled, demonstrably alive-though above his head, a monitor showed a flatlined pulse. I held a stethoscope to his warm, fragrant flank and heard, instead of the deep lub-dub of a heartbeat, what sounded like a dentist's drill or the underwater whine of an outboard motor. Something was keeping Meeko alive, but it was nothing like a heart.

As many as 3.5 million Australians suffer some form of cardiovascular condition, with over a third of those reporting oedema or heart failure, but according to the Australian Government's Donate Life website only 64 heart transplants were conducted last year. The obvious solution to this extreme scarcity is to build an artificial heart, and how hard could that be? The heart's just a pump, after all, and people have been making pumps since the Mesopotamians invented the shadoof to raise river water 3,000 years before the birth of Christ. Doctors started thinking seriously about replacing the heart with a machine around the time Harry Truman was president.

To understand why they still haven't succeeded, pick up a kilobarbell and start curling it. One kilogram: nothing. But see how long you can keep it up. Twenty minutes? An hour? Two? Your heart does that all day and all night-35 million beats a year-for as long as you live, without ever taking a rest. Manufacturing a metal and plastic heart capable of beating that way for more than about 18 months has so far proved impossible.

Instead of the deep lub-dub of a heartbeat, I heard what sounded like a dentist's drill or the underwater whine of an outboard motorThe problem is the "beating" part. Among the first to envision an artificial heart was, amazingly, the ventriloquist Paul Winchell. When not in front of a TV camera manipulating his dummies Jerry Mahoney and Knucklehead Smiff, Winchell was developing patents, some 30 in all, including one for an artificial heart that he invented with Dr. Henry Heimlich, of the eponymous anti-choking maneuver.

Back then, and up through the famous Jarvik-7-the first machine to replace a human heart, in 1982, albeit briefly-inventors could only imagine imitating the heart's lub-dub. That is, they envisioned filling a chamber with deoxygenated blood returning from the body and pumping it out to the lungs to be infused with oxygen-lub-and then drawing that good red blood back into a second chamber and pumping it back out to the body-dub.

It turns out that imitating a beating heart with metal and plastic has several limitations. First, the Jarvik-7 and its successors that are still in use require an air compressor outside the body. Through hoses that pierce the skin, the compressor fills a balloon inside one of the Jarvik's chambers, pushing blood to the lungs. Then it fills a second balloon in another chamber to push blood back out to the body.

The two balloons inflate and deflate in an alternating rhythm. It works, but it also means that a patient has to sit beside a big, noisy compressor 24 hours a day. That's better than dying of heart failure, but it doesn't make for a great quality of life. Barney Clark, the first person to live entirely on a Jarvik-7, asked his doctors several times, during his 112 days on the device, to let him die.

Clark probably would not have been able to hang on much longer in any case. Those balloons, and all other moving parts in a beating mechanical heart, wear out quickly. That's why, almost 30 years after the first Jarvik-7, artificial hearts remain what is delicately termed "bridges to transplant"-something to keep you alive until a real heart can be found.

A transplantable heart, alas, is an increasingly rare find. It has to come from a person who is in the blush of good health and also, somehow, dead. As cars have gotten safer and states have passed laws requiring seatbelts and motorcycle helmets, the number of such hearts has dwindled. The need for hearts, on the other hand, has grown with the world's population and the conquering of other diseases. And even when a heart is found, patients face the risk of tissue rejection.

Building a heart that mimics nature's lub-dub may be as comically shortsighted as Leonardo da Vinci designing a flying machine with flapping wings. Nature is not always the best designer, at least when it comes to things that humans must build and maintain. So the newest artificial heart doesn't imitate the cardiac muscle at all. Instead, it whirs like a little propeller, pushing blood through the body at a steady rate. After 500 million years of evolution accustoming the human body to blood moving through us in spurts, a pulse may not be necessary. That, in any case, is the point of view of the 50-odd calves, and no fewer than three human beings, who have gotten along just fine with their blood coursing through them as evenly as Freon through an air conditioner.

"His giant heartbeat," Rainer Maria Rilke wrote of God early in the past century, "is diverted in us into little pulses." Nowadays, maybe not.

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